Privet hedges
 

Hi all,
I'm pretty much a newbie to gardening so please forgive my brief descriptions and lack of correct names.
I am looking after someone's garden while they are away and am concerned about about three dozen privet hedges which aren't looking too good. Some are in shady areas, others are in full sun. They are all watered well, but many have a small amounts of dead branches , mainly at the base. I was told to try 'blood, fish & bone' on them, which I did. Although there are some new leaves growing, they don't seem to be doing as well as they should.
Can anyone suggest something I can do to improve their health please, maybe a fertilizer of some sort?
Thanks for any help.